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arXiv 1409.1271astro-ph.HE
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GRB内部冲击时的UHECR加速度

UHECR acceleration at GRB internal shocks

Noemie Globus, Denis Allard, Robert Mochkovitch, Etienne Parizot

摘要:

本文研究了伽玛暴内激波对CR质子和核的加速作用。物理量和它们的时间演化估计使用内部冲击模型实现的Daigne和Mochkovitch 1998年。我们考虑不同的假设的方式之间共享加速CR,e-和B场的内部冲击耗散的能量。我们的CR加速模型在温和的相对论冲击,包括所有显着的能量损失过程。我们计算CR和中微子从单个伽玛暴释放,假设原子核比质子重的相对论风。质子的最大能量只能达到~ 10^19.5 eV,而中重核的能量可以达到~ 10^20 eV或更高。从加速场逃逸的原子核的能谱很硬,而质子和中子的组合能谱则要软得多。我们使用Wanderman & Piran 2010的GRB光度函数计算了地球上预期的漫射UHECR通量。只有模型假设的即时排放代表一个非常小的一部分,在内部冲击的能量耗散,而大部分的这种耗散的能量被传送到加速CR,能够再现的大小的UHECR通量观察。对于这些模型,所观察到的形状的UHECR光谱可以很好地再现和组成的演变是兼容的俄歇所提出的趋势。我们讨论的影响,较软的质子成分的GCR到EGCR过渡的光最近的成分分析(KASCADE-格兰德实验)。相关的二次粒子扩散通量不会打破目前的观测极限。然而,来自伽玛射线暴源的扩散中微子通量应该在中微子观测站的寿命内被探测到。

英文摘要:

We study the acceleration of CR protons and nuclei at GRB internal shocks. Physical quantities and their time evolution are estimated using the internal shock modeling implemented by Daigne & Mochkovitch 1998. We consider different hypotheses about the way the energy dissipated at internal shocks is shared between accelerated CR, e- and B field. We model CR acceleration at mildly relativistic shocks, including all the significant energy loss processes. We calculate CR and neutrino release from single GRBs, assuming that nuclei heavier than protons are present in the relativistic wind. Protons can only reach maximum energies of ~ 10^19.5 eV, while intermediate and heavy nuclei are able to reach values of ~ 10^20 eV and above. The spectra of nuclei escaping from the acceleration site are found to be very hard while the combined spectrum of protons and neutrons is much softer. We calculate the diffuse UHECR flux expected on Earth using the GRB luminosity function from Wanderman & Piran 2010. Only the models assuming that the prompt emission represent a very small fraction of the energy dissipated at internal shocks, and that most of this dissipated energy is communicated to accelerated CR, are able to reproduce the magnitude of the UHECR flux observed. For these models, the observed shape of the UHECR spectrum can be well reproduced and the evolution of the composition is compatible with the trend suggested by Auger. We discuss implications of the softer proton component for the GCR to EGCR transition in the light of the recent composition analyses (KASCADE-Grande experiment). The associated secondary particle diffuse fluxes do not upset any current observational limit. Diffuse neutrino flux from GRB sources should however be detected with the lifetime of neutrino observatories.

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